Scientists stabilise vaccines for travel in tropical heat

One of the logistical problems facing doctors carrying out vaccinations in developing countries is the need to transport the vaccines either in fridges or freezers to keep them stable.

However, a team of scientists at Oxford University is working on a simple and cheap way of keeping vaccines usable even in tropical temperatures.

In a proof-of-concept experiment, the team successfully stored two different virus-based vaccines on sugar-stabilised membranes for 4-6 months at 45°C without any degradation. They claim: "The vaccines could be kept for a year and more at 37°C with only tiny losses in the amount of viral vaccine re-obtained from the membrane."

The methodology, which was developed in conjunction with Nova Bio-Pharma Technologies, sees the vaccine mixed with the sugars trehalose and sucrose. The team says: "The mixture is then left to slowly dry out on a simple filter or membrane. As it dries and the water evaporates, the vaccine mixture turns into a syrup and then fully solidifies on the membrane.

"The thin sugary film that forms on the membrane preserves the active part of the vaccine in a kind of suspended animation, protected from degradation even at high temperature. Flushing the membrane with water rehydrates the vaccine from the membrane in an instant."

Doctor Matt Cottingham, who led the research, says: "The beauty of this approach is that a simple plastic cartridge, containing the membrane with vaccine dried on, can be placed on the end of a syringe. Pushing a liquid solution from the syringe over the membrane would then release the vaccine and inject it into the patient."

But it's important to note the research is still confined within laboratory testing environments, and real-world testing could yield less satisfactory results. As Cottingham added to Wired, the experiments were carried out in controlled conditions in a lab: "Real-world temperatures would be rather different, and would also fluctuate, potentially from sub-zero to tropical temperatures. We do not yet know how well the technology will perform under these conditions."

The team also tested "vaccine vectors", which are "not yet vaccine products in their own right". These vectors are produced by using a virus as the "delivery vehicle", and a gene or genes from the disease-causing organism is then inserted into this. Cottingham explains: "A gene from the malaria parasite can be inserted into the viral vector to make a malaria vaccine, and immunisation with this viral vectored vaccine results in an anti-malarial immune response, protecting the vaccinee from malaria after exposure to infectious mosquito bites."

The team used model antigens as opposed to disease-specific genes in their tests, but Cottingham says that malaria, HIV/AIDS and tuberculosis vaccines created using this methodology are currently in clinical trials.

But when these vaccines are ready, and the Oxford team's thermostabilisation technology has been proved safe for humans, Cottingham argues that it is feasible that a medic could take vaccine doses to remote villages in just a backpack. It would be a radical result if successful, but there's much work to be done before such a scenario could be considered for real-world use.

Nova Bio-Pharma has already developed a prototype all-in-one ready to inject delivery device, which consists of a supporting housing for the membrane inserted in between the syringe and the needle. This is currently being developed to meet British safe practice standards.

"Our overall aim is to link the thermostabilisation technology with these advanced vaccine candidates so that we can achieve a double breakthrough: new efficacious vaccines that can be deployed in a thermostable formulation in remote areas of the developing world, where infectious diseases wreak the most damage," he says.